Compared to other programming languages, installing Scala is a bit unusual. Scala is unusual because it is usually installed for each of your Scala projects rather than being installed system-wide. Both of the above options manage (via sbt) a specific Scala version per Scala project you create.

But it's also possible to "install" Scala in numerous other ways; e.g., grab Scala binaries and use Scala from the command line or use Scala in your browser!